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I use CA glue† very frequently in my shop, but I'm not entirely sure how it works. I've noticed three main modes of curing, I've emphasized the key observations:

  1. When dispensed, it will remain fluid until even a small amount of pressure is applied. With pressure, it will set and cure in 5 - 45 seconds. Often, depending on the materials, it remains completely clear after curing.
  2. If a drop of it is left out undisturbed (also applies to glue that may have been squeezed out of the joint), it will cure after a relatively long time, on the order of 20 - 60 minutes. If it cures in this way, it will develop a white crystalline substance (ranging from on-the-surface-only to the entire drop). This structure is hard and brittle.
  3. It will cure in the bottle after a very long time, on the order of months or years (depending on whether or not the bottle has been opened). When it cures this way, it remains clear. It also becomes hard and brittle, but seems to have a higher strength than the white crystalline form.

So; here's what I know about it and some other factoids I found in research:

  • The active chemical in most consumer-grade CA glues† is ethyl 2‑cyanoacrylate (CAS 7085‑85‑0).
  • Generally, it's present in the glue at a concentration of 60% to 100% by weight.
  • It emits very strong, irritating, noxious fumes as it cures, but is odorless after cure.
  • I know that curing is some type of polymerization and is a reaction with water.
  • † It seems "CA" has either become a misused colloquialism, or is used to refer to the entire class of cyanoacrylate glues (e.g. "ECA" appears to be the technically correct abbreviation for ethyl 2‑cyanoacrylate). I actually didn't even know there were different types until right this moment (hence the awkwardly placed †'s, heh).

So my question is, basically: What is going on here? In other words: How, exactly does it cure? Why does pressure seem to be involved? What is the white crystalline substance and why does it only form in certain situations? What are the fumes? What is the reaction here? All the details.

I'm looking for a detailed answer, as much as possible -- for example, I already know from the Wikipedia page that it polymerizes in presence of water. What I'd like to know is some more advanced information about how and why that reaction takes place, energies involved, intermediates, crystal structure, what causes my observations, etc. I'm not a chemist but hit me with all the jargon, I could stand to learn a few new words.

I'm actually not particularly interested in how it reacts with the materials it is applied to or how it achieves adhesion, I'm much more interested in the curing process itself.

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    $\begingroup$ There is a simple observation that explains the process. The cyanoacrylate can undergo a chain reaction to form a strong polymer. That reaction is tuned to be triggered by interaction of the glue with water. Most surfaces have adsorbed water in enough quantities to initiate the reaction and, once started, it proceeds until the whole mixture has been polymerised into a strong polymer forming a bond. I'll leave the details to others to fill in. $\endgroup$
    – matt_black
    Commented Apr 29, 2021 at 20:52
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    $\begingroup$ Look up “anionic olefin polymerization” $\endgroup$
    – Andrew
    Commented Apr 29, 2021 at 21:22

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